I have a web the project from realisation a pool connection (GlassFish+DB2). Behind time reboots mainframe which it is established СУБД DB2 and after that when the user starts a web the application connection is not created new and the error stands out:

Is that so strange? The connection to the database is cut, so you'll get connection errors.

The question is: even when you get the error(s), does the connection pool create new connections so the web application will work anyway? Because if not you will probably want to look in the glassfish manual how you can configure the connection pool to do that.